ACTIVE ISOLATION OF STRUCTURAL VIBRATION ON A MULTIPLE-DEGREE-OF-FREEDOM SYSTEM .1. THE DYNAMICS OF THE SYSTEM

This paper is the first of two companion papers concerning the active control of structural vibration in an isolator system. A preparatory s tudy is reported of the passive vibration transmission, which is evalu ated in terms of power, considering a multi-mount and multi-degree-of- freedom isolator system with passive mounts. The modelling of the syst em is based on a matrix method which uses mobility or impedance repres entations of three separate elements: the source of vibration, the rec eiver and the mounting system which connects the source to the receive r. A detailed description of the mobility or impedance formulae is giv en for a rigid mass oscillating in a plane (the source), for a beam on which flexural and longitudinal waves propagate (the mounts) and for an infinite or finite plate in which in-plane shear and longitudinal a nd out-of-plane flexural waves propagate (the receiver). It is shown t hat at low frequencies any ''rigid body mode'' (axial-mode, transverse -mode, pitching-mode) is capable of transmitting considerable power to the receiving system, while the transmission of vibration at higher f requencies is mostly related to the dynamics of the distributed mounts or receiver. (C) 1997 Academic Press Limited.